Metal forming



Oct. 17, 1961 N. A. KEITH ET AL 3,004,327

METAL FORMING 2 Sheets-Sheet 1 Filed March 17, 1960 FIG. 2 FIGB FIG. 4

INVENTORS.

NORVAL A. KEITH GLENN E KOERTGE LESTER J. TRANEI.; rm-:RON F. PAuLs N. A. KEITH ETAL 3,004,327

METAL FORMING Oct. 17, 1961 Filed March 17, 1960 2 Sheets-Sheet 2 FIGS FIG@ INVENToRs. Nom/Al. A. KEITH GLENN E. KOERTGE LESTER J. TRANEI. THERo/v F PAI/LS United States Patent O 3,004,327 METAL FORMING Norval A. Keith, East Alton, and Glenn E. Koertge, Al-

ton, lll., and Lester J. Tranel, St. Louis, Mo., and

Theron F. Pauls, Alton, Ill., assignors to Olin Mathie` son Chemical Corporation, East Alton, Ill., a corporation of Virginia Filed Mar. 17, 1960, Ser. No. 15,572 18 Claims. (Cl. 29-157) jacent sheets. This resultant structure, containing the system of passageways, can be obtained by a process such as that disclosed in the patent to Grenell, U.S. No. 2,690,002, granted on September 28, 1954.

In the process of the aforesaid patent, a pattern of weld-inhibiting material is applied to a clean surface of a sheet of metal. A clean surface of a second sheet of metal is superimposed on this surface and the two sheets are secured together to prevent relative movement between them and then pressure welded together, as by hot rolling, in the adjacent areas thereof which are not separated by the weld-inhibiting material. The welding `of the sheets results in a substantial elimination of any interface between the superimposed sheets except in the areas defined by the weld-inhibiting material so as to provide a substantially seamless or solid integral sheet. Subsequent to the Welding operation, the resultant blank or sheet is usually softened as by annealing to make it more pliable, and if desired, cold rolled and again softened by annealing. As noted above, the weld-inhibiting material results in an unjoined portion between the outer faces or surfaces of the sheet metal blank. After softening the blank, the unjoined portion is expanded by injecting therein a fluid pressure of sumcient lmagnitude to permanently distend in the area of thetunjoined portion to form the desired pattern of passageways. As disclosed in the aforesaid patent, the distentionmay be done in varied manners so that the expanded system of passageways will bulge either out of one or out of both faces of the sheet metal blank.

For some applications, as in U.S. Patent-2,740,188, granted April 3, 1956, it is sometimes desirable to distend at least a portion of the unjoined areas in the sheet metal blank by mechanical means such as a mandrel. In other applications, it is often desirable, irrespective of the manner in which the sheet metal blank is distended, to further size the distended passages to obtain the contiguration and dimensions required. Generally with such mechanical distentions or sizing operations no difiiculty is encountered when the sheet metal blank is fabricated of metals having the same physical characteristics. However, in sheet metal blanks formed of component metal sheets, such as a hard and a soft sheet, due to a dilerence in their physical properties, such as in the elastic limits of the metals, heretofore conventional methods and tools for mechanical distention have proven inadequate.V Such conventional tools force the softer metal of the blank to become distended to a greater tube height than the harder metal whereby the softer metal is bulged out of the faces of the blank a greater amount than the harder metal. Due to these disadvantages, it has been diliicult or impossible to control the Bi?? Patented 0st. 17, 1961.`

distention, of the tubular passageways so as to obtain precision in the configurations desired.

Accordingly it is an object of this invention to` provide a novel tool and process eliminating disadvantages of the prior art.

Another objectof this invention is to provide a novel tool and process for mechanically distending tubular passageways contained in la metal tube sheet formed from complementary sheets of diverse metals.

Another object of this invention is to provide a novel tool and process for mechanically sizing a tubular passageway contained in a metal sheet formed from complementary metal portions having different physical characteristics. t v

A further object of this invention is to provide a novel tool and process for controlling the mechanical distention of a tubular passageway contained in a metal tube sheet formed from complementary metal portions having dfferent physical characteristics.

A still further object of this invention is to provide al novel tool and process for the mechanical sizing of a tubufrom metal complementary portions having different elastic limits.

Other objects and advantages will become more apparent from the following description `and dra-wings in which:

FIGURE l is a side elevational view of a tool illus- Itratingan embodiment of this invention together with a perspective View of a portion of a distendable panel shown partly in cross-section;

FIGURE 2 is a sectional view taken along lines II-II in FIGURE 1;

FIGURE 3 is a cross-sectional view taken along lines III-III in FIGURE l;

FIGURE 4 isa sectional view taken along lines IV-IV l in FIGURE l;

FIGURE 5 is a perspective view of the tool or mandrel illustrated in FIGURE l shown entering a distendable panel;

FIGURE 6 is a side elevational view of a tool illustrating another embodiment of this invention -in conjunction with a perspective view of a portion of another -distendable panel partly in cross-section;

FIGURE 7 is a side elevational view in section of the tool or mandrel of FIGURE 6 shown within the distendable panel of FIGURE 6;

FIGURE 8 is a cross-sectional View taken along lines VIII-VIII'in FIGURE 7;

FIGURE 9 is a sectional view taken along lines IX-IX in FIGURE 7;

FIGURE 10 is a perspective View of a portion of the indatable panel in FIGURE 6 subsequent to mechanical distentions.

FIGURE ll is a side elevational view of a type of tubular conduit in a distendable panel for illustrating another embodiment of this invention;

FIGURE 12 is a side elevational view in section showing the distention of the panel of FIGURE 11 in accordance with another embodiment of this invention; and

FIGURE 13 is a perspective view of a portion of the inflatable panel of FIGURES l1 and 12 subsequent to mechanical distention.

- In accordance with this invention it has been discovered that in panels or tube sheets formed of a softer cornponent sheet superimposed upon a harder component sheet, whereinV the difference in hardness may result from the difference in elastic limits of the components, in which the adjacent areas of the component sheets are selectively welded together in a pattern defining a desired system of passageways, controlled distention of the passageways 'can be obtained by regulating the distending force on the softer metal relative the force of distention applied on the harder metal by means of a tool and a novel method of distention. The controlled amount of distending forces on the respective component sheets is obtained in accordance with this invention by a mechanical punch or mandrel having correlated configurations provided in its working portions for the distention of the component sheets inthe expansion or sizing of the passageways contained in the blank. The working portions of the tool of this invention are provided with oppositelydisposed bearing surfaces for application of the distending forces againstv the harder sheet and against thefsofter sheet. The working portion of the mandrel will have its crosssectional configuration dimensions corresponding to the cross-sectional configuration. desired to be imparted in the distendedl tubular. passageway. And-, the amountV of distention desired in each sheet is obtained by controlling the amount of area of the bearing surface pressing against the softer metal relative tothe amount of area of the bearing surfacepressing against the harder metal component sheet. To obtainv such controlled distention the ratio of the area of thebearing surfacepressing against the softer sheet to the area4 of the bearing surface pressing against the harder sheet is regulated to. equal the ratio of the elastic limit of the harder` sheet tothe elastic limit of the softer sheet multiplied by.v the` ratio' of` the amount of distention desired inv the.A softer sheet.y to the amount of distention desired in the harder. sheet, and further multiplied; by the, ratio of the thickness of, the softer sheet tothe. thickness of the.y harder sheet.

As will be understood the specic numerical areas-.of each bearing surface will necessarily be dependent either on personal preferences, orl on the specific dimensions. of the tubular passageway to beA distended; For example, whereas both areas of the bearing surfaces may be large when applied to distentionof tubular passageways of large cross-sectional dimensions, in contrast bothy areas: of the bearing surfaces,willnecessarily be relatively smallwhen applied to the distention of tubular passageways. of relatively small cross-sectional dimensions.

Regulation or control of the ratio of bearingk surfacesV given above is applicable toany combination. of metals, amount of distention desiredy in each andzthe thicknesses of each, but become simplified with the equalization With the amountr of distention desiredl and/or in the` thicknesses o f the metal component sheets. IFor example, if` thev amount oft distention of a, tubular passageway in a tube sheet is to be equal-so thatA the distendedtubular passageway will` be bulged equally out of thefaces of the tube sheet, the ratio of the bearingsurface pressing against the softer sheet to the areaofl the bearingsurfacepressing against-the` harder sheet will'- then be equal to the ratio of the elastic limits ofthe harder sheet to the elastic limits ofthe softer sheet multiplied by the ratio of the thickness of the softer sheet to be distended to the ratio of the harder sheet to be distended. Where, in addition, the thicknesses-of the'componentsheets to` be distended are equal to the ratio of the arca of. the. bearing surface pressing against.the softer sheet to the; area o f, thebearing-surface pressing the hardersheet will. be merely equal to theratioof thelelastic limits of the harder` sheetito the elastic limitsof the softer, sheet. The term elasticlimits is employed in thisapplication in itsac-f cepted sense todefine the maximum. stress that amaterial` will withstand; without permanent deformation,- andd in. practical sense; is.v used interchangeably withY the, term yield strength.

Morespecically by reference tothe drawings, in FIG- URE. 1, there isshown artool 1 and aninilatabl panel.

2` formed fromtwoA superimposedcomponent metal sheets 3. and 4, having, different elastic limits; Tle adjacent' areas offsheets, 3 and'4lare selectively. welded`together` inapatternto provide, a systemof embryonic passagieways. S, disposed between-,unjoined portions A6 and'T and laterally. defined between.,parts of the, Welded. portion 8.

Any combination: of metals, of different. elastic limits weldable to each other may be employed, for example, such as the different alloys of the same base metal' which in the preferred embodiment-'may be exemplified in the pressure welding of 1100 type aluminum alloy to 3004 type aluminum alloy, both alloy designations in accordance with the Aluminum Association standards. For the above specific alloys, 1100 type' aluminum alloy has an elasticlimit or yield strength of- 5,000v p.s.i. and the 3004 type aluminumY alloy has an' elastic limit or yield strengthof 10,000 psi.

In order -to provide for the inationof the system of embryonic passageways 5, a strip. or'unjoined portion 9 of panel 2, definingx a corresponding embryonic tubular passageway, extends to the edge of the panel at 10 to provide a line of separation 11.

The tool: or mandrel I is provided' at the" front end of a shank or shaft 11 with' a working portion 12 having oppositely disposedk complementary bearing surfaces 13 and 14 which` will press againstv the unjoined portions, ininlet strip 9, of component sheets 3=andv 4, respectively, and? distend the inlet strip orV passageway 9 into the desired cross-sectional configuration so asl to, for example, facilitate the attachment ofi any appropriate inflation nozzle; In order to facilitate the insertion of tool 1 into the passageway 9fthe1working portion 1-2.is provided with any conveniently: shaped point 15 to initiate the initial separation of the unjoined portions. Attached to the rear portion of shank or shaft 1.11* is any convenientlyl shapedhandle 16 whichmay be handv gripped for manual insertion oflthe mandrelwithin passageway 9:

Tofinitiatethe distention of panel 2, the point 15 ofthe tool 1A maybe manually. inserted into the laminated or unjoined: strip'9 atl the line of separation, 11f` Lf' desired, theunjoined portionf of. the panel' opposite this line of separation may be.y provided with an initial opening by anyconventional means, asaforI example, by the teachings of U.S.' Patent' No. 2,835,025 granted on May 20, 1958, to further facilitate lthe introduction of' the. distendingv tool into the unjoined strip. 9. With the pointll'; of the tool inserted 'ini-the unjoined strip l9,-' lthe tool is: then manually forcedfurtherL intozthe panel to. a depth .suicient' to accomplish thedistention desired. Itl is tobe understood. that although the. tool has been described forv manual operation, the toolmay also and preferably, althoughnot illustrated, take the form-of adrift' punch which may be drivenA into= the unjoinedstrip 9i by any` conventional vibrating tool:

Aspointed outv above, the working 1portion 1-2 may have any cross-sectional configuration desired correspondingV tothe desired distended-configuration torbeimparted in. passageway 9i In-the embodiment illustrated,the workingaportionllZ is .provided with a coniigurationto impart a substantially circular cross-section in passageway 9.

. Accordingly, Ithe front and lower -p'art ofthe Working portion 12 hasv asemi-cylindricalconfigurationfmerging into a rearwardly disposed portioninwhich the cross-sectional coniiguration'iscylindrical; In effect; the lower Lhalfof! the working portion-12 will fornr a.. semi-solid cylinder from-which` projects `arsemi 3f-linderl of, shorterlength to form the upper partv off working portion 12, which together provide a circularV distended configuration in passageway 9 Since in-mandrels employed for providing circularz configuration', the peripheries off the upper and lower parts will-be `substantially equal, the area ofthe bearingsurface will be controlled and regulated-by theirl length-along'toolll. In-the embodiment'shown the-shankorvshaftll playsno part in thedistention of passageway 9-1 and'ispreferably designedi so as not to exert anyy force against the' walls oflpassage 9, a11d f`orconvenence has been illustrated asof an*elliptical-configuration-disposed'in a horizontal plane:

In FIGURE 5'; the' working portion' 12 of tool or mandrelv 1 is sh'own partially inserted, as for example manually, within the embryonic passageway` 9`of panel 2. whereinbearing-,surfce 14 ispressedlagainst the unjoined portions of conponent sheet 4 opposite passageway 9 and bearing surface 13 presses against the unjoined portions of component sheet 3 opposite passageway 9. The amount of the areas of the bearing surfaces pressing against the respective unjoined portions on which they act will determine the areas of the unjoined portions on which the distending force will react to thereby regulate the distending pressures actingon the unjoiued portions opposite their respective bearing surfaces. For example, with a tube sheet formed from a component sheet of 1100 type aluminum alloy pressure welded to a component sheet of 3004 type aluminum alloy, in which the unjoined portions are of substantially equal thickness so as to dispose the unjoined portions midway between the outer faces of the tube sheet, where equal distentions of complementary unjoined portions are desired, the ratio of the bearing surface to each other will be substantially equal to the inverse ratios of the yield strengths of the respective alloys on which they will act.

Specially, employing theelastic limits or yield strengths of the above aluminum alloys, the ratios of the bearing surface pressing or acting on the 1100V type aluminum alloy to the area of the bearing surface pressing on the 3004 type aluminum alloy will be substantially equal to the inverse ratio of the elastic limits of the respective alloys, that is 10,000 p.s.i. 5,000 p.s.i.

which is equal to a numerical ratio of 2. Accordingly, the area of the bearing surface on 1100 type aluminum alloy will be 1/2 times the area of bearing surface acting on the 3004 type aluminum alloy. Where the embryonic passageway 9 of this specific panel has an initial width of 0.225 inch and is to be distended to a circular crosssectional configuration having a diameter of 0.223 inch the area of the bearing surface acting on 1100 type alloy may be substantially 0.04375 square inch while the area of the bearing surface for distention of the 3004 type aluminum alloy may be 0.0875 square inch.

As indicated above, the invention is equally applicable to the sizing of partially or fully formed tubular passageways such as 18 in FIGURE 6. Passageway 18 is part of a distended system of passageways 19 formed between the pressure welded component sheets 20 and 21, for example as by the aforesaid U.S. Patent 2,690,002, which as discussed above, involves interposing a pattern of stopweld between superposed metal component sheets, pressure welding and followed by inflation with distending pressure injected within the resultant pressure welded tube sheet. When the panel is fabricated, according to the process of the aforesaid patent, from metals having different elastic limits, the resultant blank or -tube sheet upon inflation with fluid pressures, will be distended unequally in proportion to the elastic limits of the complementary portions defining lthe unjoined portions in the tube sheet. In sizing tubular passageway 18 of this emr bodiment, the complementary bearing surfaces of each working portion may be correlated so as to equalize the distention of the unjoined portions defining tubular passageway 18 whereby the walls of passageway 18 will be bulged equally out of opposite faces of the tube sheet. Such eqgualized distention of tubular passageway 18 facilitates' the insertion of an appropriate connecting means from the tube sheet to other parts of a fluid system, for example, as in'refrigerating systems.

In the specific embodiment shown, the distended tubular passageway 18 is sized sol as to provide on different portions thereon progressively increasingly larger crosssectional configurations. Such sizing is accomplished with a sizing tool 22 provided with a series of working portions 23, 24 and 25 disposed in spaced relationship to each other along the shaft or shank 26 of the tool. Each successive working portion, 231, 24 and 25, will have progressively greater cross-sectional configurations corresponding to the cross-sectional configurations desiredto be imparted in the tubular passageway 18. In each working portion the ratio of the bearing surf-ace bearing on the softer metal to the area of the bearing surface acting on the harder metal will be determined as in the preceding embodiment.

To obtain the desired sizing of distended passageway 18, tool 22 is inserted into tube sheet 23 between the unjoined portions of the tube sheet defining the tubular passageway 18. The resultant sized tubular passageway 18 will have successive portions of progressively increased cross-sectional configurations. Thus, tubular passageway 18 will have a portion 27 having a cross-sectional configuration thesame as the initial cross-sectional configuration of passagewayv 1.8, a .portion 28` having an enlarged cross-sectional configuration imparted to it by working portion 23 of tool 22 and a portion 29 having a further increased cross-sectional configuration imparted to it by the working portion 24 of tube 22 and a portion 30 having a still further enlarged cross-sectional configuration. i

Although the invention has been described in the preceding embodiment relative to embryonic or distended passages having initially uniform dimensions, it is equally applicable to the distention and sizing of passageways initially provided with a restriction, as for example by the process in U.S. P'atent 2,822,151, granted on February 4, 1958. Such a configuration may be obtained by designing the pattern of weld-inhibiting material interposed between superposed component sheets so that a'passageway narrows along its axis and then enlarges to its original dimensions. Upon pressure welding and expansion of the passagewaysV between the sheets, the aforesaid passage will have portions 31 distended 'to' a cross-sectional configuration corresponding to the initial dimensions of the stop-Weld defining this portion and a constricted portion 32 corresponding to the narrowed portion ofthe stop-weld defining this portion of the passageway. As in the preceding embodiments, the fabrication of tube sheets initial expansion thereof with iuid pressure will cause unequal distention of the unjoined portions of theV tube -sheets in proportion to their elastic limits. A tubular passage 33 of this tube sheet containing tubular portions 31 and 32 may be further mechanically distended 'with a tool 34 so as to both equalize the distention and/or to adapt the tubular passage 33 for the reception of various connecting means. To accomplish this, sizing tool 34 is provided with two' Working portions, a working portion 35 for the sizing of constricted portion 321 and a working-portion 36 for the sizing of tubular portion' 31. As

will be understood, the cross-sectional dimensionsof the working portions and the ratio of the complementary bearing surfaces in each working portion will Vbe correlated to each other as in the preceding embodiments. The resultant sized tubular passage 33 will have in the restricted tubular portion 32' a part 37 thereof corresponding to the initial dimension of constricted portion 32 and a sized part 38 thereof correspondinging to the dimensions imparted to` it by working portion 35. of sizing tool 34. In like manner, the tubular portion 31 of tubular passage 33 will have a part 39 thereof corresponding tothe initial dimensions of tubular portion V31 and a part 40 having the cross-sectional dimensions imparted to it by working. portion 36 of tool 34.

Although the invention has been described with reference to specific embodiments, materials and details, various modifications and changes, within the scope of this invention, will be apparent to one skilled in the art and are contemplated to be embraced within the invention.

What is claimed is: Y

1. The method of mechanically distending a tubular passageway of a metal tube sheet formed by selectively welding, in a pattern defining a system of passageways which comprises at least said passageway, areas of` adjacent surfaces of superimposed sheets of metals having dilerent elastic.v limits wherein. said welding denes said passageway between opposed unioined portions of said sheets and laterally between-y welded` portions of. saidl sheets;` said method comprising inserting between saidunjoined portions a. mandrel having. a cross-sectional` configuration corresponding to the desired distendedv cross-sectional.:congurationtof'saidl passageway said mandrel having: andsaid insertion: beinglmade so as tolapply ai first. bearing; surface oppositey and adjacent one of. said` unjoined. portions; havingi the lower elastic limitf, andy an# oppositely' disposed? second; bearing surface opposite. andy adjacent. the other ofi said unjioined portions having@ the higher` elastici limit. wherein: the' ratio: of. the area'\ of-`V the bearing: surface; opposite and adiacent'- saidY one unioined portion totthe: area" of the bearing surface'. opposite and adjacent saidv other. unioined portion= is equalY tothe 'ratio ofrsaid? higher elastic limitto thesaid lower elasticlimit the-ratiol off theI amount; of.' distention. desiredv in? saidone unioinedaportion: to; the amount' of.' distention desiredinf. said otherfunioined. portion: times ratio of the thickness of said one unjoined portion to the thickness of the other said: unjoined portion;

2'.. The. method` of claim'y 1. whereiny said sheets are; ofi differenti alloys having. thel same base metal.

3;. The: method of. claim. Zwherein. said sheets are of differenti alloysv of aluminumz.

' 4:.. 'lhesmethodf off claim` 1i 'whereinl the thicknesses of said unjo'inediportionsare equalf and wherein the ratiorof? thearearof thebearingfsurface opposite andA adjacent said onel unjoined: area to the areal of. the bearingf surface opposite andi adjacent. said. other.` unionedportion is equalto: the; ratio ofsa-idfhigher elastic'limit toi said? lower velastic limtltimesthe ratio-ofthe amount* of distention desiredi in` said. one'.l unioined portiony to. the amount of distension desiredinsaid-5 other' unioinedL portion;-l

-5. vmethod. for mechanically distendin'g tubular' passageway of.' a-metalr tube sheet.` comprising selectively- Welding'. inlay. pattern defining' a system offemb'yronic passageways containing'iat least one embryonic passage- 'wayf corresponding'rto. said tubular! passageway, areasof' adiacenti. surfaces.I of' superimposed sheets of dilferent metalsihavingfdifferent elastic limitslwherebysaid weld'- ring'A denes.v said.l embryonic I passageway between'y opposed unioined portions ot said sheets and" laterally between welded portions; of saidi sheetsg.. inserting between said` unjoined portions dn'eiining"said` embryonic passageway a mandrel) lziavingi working? portions thereon corresponding to'fthe tdesired'crosslseotionalconiiguration off Asaid tubular' passageway; said lWorkingA portion having` and said i11- sertionf being.:-niadel so as' to applyf af' rst bearing sur-face `r opposite andi adiacenti onev of said unjofinedl portions l'hav in'glthelower? elastic limitand'I oppositely disposedl secondY bear-ingi surfaceA5 opposite' l and' adiacenti theA other! of?v said unioin'edlpottionsliaving? the' higher elastici limiti wherein the ratiovoff the area oitlie'y bearing 'surface opposite and adiacenti said? onebunjoinedporrtion to the area ofthe bearin'gsurfaceopposite A'and' adjacent' said f other' unjoined portion' isveq'u'altotlielrratic's of said higherfelastic' limit tot thev saidi lower ela'stic'rliinit times` the ratiol of the' amount' of distention desired'Vv insaidf others unjoined portion; timesfthe ratio ofzthe thickness `ofl said" one unjoinedi portion. to the'thickness' ofthe saidoth'erunioined Y portion.'

6.1 Themethod'of claim' 5: wherein said sheets are of differenti alloys havingthesame base metal-.-

saifdrone-lunioinedarea to rthe area ofI the bearing surface oppositevand-sadiacent: saidzotherunioined portion is* equal toitheratiofof saidfhigherelas'tic limit tolsaidlowerrelstic limiti times: the ratiolfof the. amount `Vof]A distention desired inf saidon'e unioined portion@ to the Iamount' of distention' desiredv in"A said other unjoin'ed portion;v

9L The method of claim"Siwherein'saidlsheetsfare ofdi-fferentv alloys having. the same base met'alfi 10: rFhernethod ofclaim 9 Whereinf said sheets are of diterentalloysof aluminum;

' ll. A method forV mechanically distending tubular passageway ora metalf tube` sheet comprising selectively weld'- ing, ina patternrdelining a system of' embyronic passage'- ways-containing at least one embryonic passageway corresponding to said tubular passageway, areas of adiacent surfaces of superimp'osedsheets o'f differentv met-als having dfieren-telastic' limits wherebysaidwelding deiines said embryonicl systemf of passageways between opposed unjoined'portions of said sheets and'- laterally between welded portions-of said-sheets,r injecting along saidsystem of embryonic passageways-suliicient iluidL pressure to permanentlyz distendJ and bulge portions-of! saidl slieet-y opposite said` passageways out of the faces of saidsheets to form a. corresponding system ofpassagewaysl including said tubularV passageway' whereby the portions ofy said sheetsy having' thelcwer elasticlimit opposite saidpassageways areA distend'edvandl bulges a greater amount' than the portions of said sheets having the higher elastic limit opposite said tubular passagew-ays, sizing said passageway by inserting into said tubular passageway between thecorresponding unioined portions-thereof a sizer mandrel corresponding to the desired sized cross-sectional conguration of said tubular passageway, said lworking portions having and' said' insertion being" made so as' to applyV a first bearing' surface opposite andl adjacent one of said' unjoinedportions of said tubular passageway' having the" lower elastic limit and an' oppositely disposed-secondbe'aring surface opposite and adjacent' the other. ofV said' un-y joined portions of said' tubular passageway' having the higher' elastic limit wherein the ratio" of the area' of the' bearing surface' opposite and' adjacentV said one unioinedI portion lto the area of the bearing surface opposite and adjacent said-other unioined portionisequ'al to theratio of said higher elasticA limit' t'ov the s'aid lower' elastic limit times theratio of the amount of distention desired in said one Yunioined portion to the amountof'disten'tion desired in' sardothe'r unjoined portion times ratio'of thefthicknessof' saidoneunioin'ed portion'to the thickness of the'other' said' unicined portion.

12. The method' of claim" 1l' wherein said-sheets are" ofv different alloys having the same basemetal 13; The methodof claim l2 whereinf said sheets' are' of diierent alloys of aluminum.

14. The method of claim l1 wherein the' thicknesses of said unioined portions' `defining said tubular passageway are equal Iand'Wherein the'ratio ofthe arearof the bearing" surface lopposltean'dadjacent'sad one'unioined 'area' 'to the area ofthe'bearing surface oppositeand adjacent saidone unjoined area'to the area of` thebe'aring surface'opposite said other unjoined portion is equal to tlie'ratio of'said higherv elastic'limit' -t'o s'a'idlower elastic limit times the ratioof` tlieamountv of distention desired'insa'id one u'njoincd portiontothe' amount of'distentiondesir'ed'in said otherseparatedportion'.

15. The method of'claim 147whereir'1' said'sheets areof dilerent alloys havingthe same' base metal.

16. The methodofc'laim' 15 wherein said'sheets'are o'f` different alloys ofaluminum'.' j

l-7. AV mandrel for mechanically Vdistending a tubular passageway of ametaltub'e sheet formed by selectively welding,l in la"patter`n defining a system of' p'assagewaysy which' comprises atleast saidpassageway, areas of adjacent' surfaces oisuperirrposed sheets-of differentmetals having ldifferent Aelastic limits wherein saidwelding defines said passageway between' opposed unioined portions of said working portion having a rst bearing surface for application opposite and adjacent one of said unjoined portions having the lower elastic limit and a complementary oppositely disposed second bearing surface for application opposite and adjacent the other of said unjoined portions having the higher elastic limit wherein the areas of both said bearing surfaces are unequal with the ratio of the area of the bearing surface opposite and adjacent said one unjoined portion to the area of the bearing surface opposite and adjacent said other unjoined portion equal to the ratio of said higher elastic limit to the said lower elastic limit times the ratio of the amount of distention desired in said one unjoined portion to the amount of distention desired in said other unjoined portion times 10 the ratio of the thickness of said one unjoined portion to the thickness of the other said unjoined portion.

18. The mandrel of claim 17 including a series of Working portions in spaced relationship to each other with each successive portion having progressively greater crosssectional coniiguration.

References Cited in the file of this patent UNITED STATES PATENTS l0 2,493,127 Franck Jan. 3, 195o 2,662,273 Long Dec. 15, 1953 2,740,188 v Simmons Apr. 3, 1956 2,850,796 Kaplowitz Sept. 9, 1958 

1. THE METHOD OF MECHANICALLY DISTENDING A TUBULAR PASSAGEWAY OF A METAL TUBE SHEET FORMED BY SELECTIVELY WELDING, IN A PATTERN DEFINING A SYSTEM OF PASSAGEWAYS WHICH COMPRISES AT LEAST SAID PASSAGEWAY, AREAS OF ADJACENT SURFACES OF SUPERIMPOSED SHEETS OF METALS HAVING DIFFERENT ELASTIC LIMITS WHEREILN SAID WELDING DEFINES SAID PASSAGEWAY BETWEEN OPPOSED UNJOINED PORTIONS OF SAID SHEETS AND LATERALLY BETWEEN WELDED PORTIONS OF SAID SHEETS, SAID METHOD COMPRISING INSERTING BETWEEN SAID UNJOINED PORTIONS A MANDREL HAVING A CROSS-SECTIONAL CONFIGURATION CORRESPONDING TO THE DESIRED DISTENDED CROSS-SECTIONAL CONFIGURATION OF SAID PASSAGEWAY SAID MANDREL HAVILNG AND SAID INSERTION BEING MADE SO AS TO APPLY A FIRST BEARING SURFACE OPPOSITE AND ADJACENT ONE OF SAID UNJOINED PORTIONS HAVING THE LOWER ELASTIC LIMIT, AND AN OPPOSITELY DISPOSED SECOND BEARING SURFACE OPPOSITE AND ADJACENT THE OTHER OF SAID UNJOINED PORTIONS HAVING THE HIGHER ELASTIC LIMIT WHEREIN THE RATIO OF THE AREA OF THE BEARING SURFACE OPPOSITE AND ADJACENT SAID ONE UNJOINED PORTION TO THE AREA OF THE BEARING SURFACE OPPOSITE AND ADJACENT SAID OTHER UNJOINED PORTION IS EQUAL TO THE RATIO OF SAID HIGHER ELASTIC LIMIT TO THE SAID LOWER ELASTIC LIMIT TIMES THE RATIO OF THE AMOUNT OF DISTENTION DESIRED IN SAID ONE UNJOINED PORTION TO THE AMOUNT OF DISTENTION DESIRED IN SAID OTHER UNJOINED PORTION TIMES RATIO OF THE THICKNESS OF SAID ONE UNJOINED PORTION TO THE THICKNESS OF THE OTHER SAID UNJOINED PORTION. 